Order of Magnitude

What physicists typically mean by the term “natural” is that we expect reasonableness in the laws of physics. Let us start with examples drawn from daily life. Let us ask, for example, how many people have you shaken hands with ¹ in the past week? Maybe 5, 10, or 20? Physicists would estimate this number, lying somewhere between 1 or 100, as being on the order of 1, which we abbreviate as O(1) . It is possible that you somehow shook hands with thousands of people–if you happen to be a politician seeking reelection, for instance, or a celebrity at multiple book signings. Or maybe you shook no hands at all. But this general number, O(1) , is most likely in the right ballpark.